Metal oxide semiconductors, such as zinc oxide (ZnO) and indium gallium zinc oxide (InGaZnO) are attractive for device fabrication due to their high carrier mobility, low processing temperatures, and optical transparency. Thin film transistors (TFTs) made from metal oxide semiconductors are particularly useful in active-matrix addressing schemes for optical displays. The low processing temperature of metal oxide semiconductors allows the formation of display backplanes on inexpensive plastic substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). The transparency of oxide semiconductor TFTs leads to improved pixel apertures and brighter displays. In contrast, amorphous silicon (a-Si) TFTs reduce pixel aperture because a-Si devices are light sensitive and must be shielded from the light.
Although metal oxide semiconductor TFTs have great potential due to their transparency and the potential for high performance devices formed at or near room temperatures, fabrication of stable devices remains a challenge. Metal oxide semiconductor TFTs may exhibit hysteresis in their characteristics as a function of gate-bias. Development of metal oxide semiconductor technology is ongoing, and current efforts are focused on reducing or eliminating hysteresis to enhance TFT stability. The present invention fulfils these and other needs, and offers other advantages over the prior art.